In the related art, there is a thermal printer that prints on heat sensitive paper by heat generation from a thermal head. In the thermal printer, when temperature around the thermal head decreases, even if heat is applied to the heat sensitive paper, since the thermal head is cooled by its surroundings, the printing result may be of low printing density or blurred. Accordingly, in the related art, in order to improve printing quality in low temperature environments, the width of an electric power pulse output to the thermal head is increased by decreasing the transporting speed of a recording paper.
In addition, the above-described thermal printer may be a portable type printer using a battery as a driving power source. In such a battery-driven printer, electric power that can be supplied at one time is limited. Therefore, in such a device, heat generating elements making up the thermal head is driven in a time division manner, in accordance with a printing coverage for each line. In particular, the transporting speed of the thermal head is changed according to the printing coverage. Thus, as the printing coverage increases, the number of time divisions for driving the thermal head increases, and thereby the transporting speed of the recording paper, that is, the printing speed, decreases.
In addition, because the battery-driven printer is portable, it can be used in various environments such as low temperature environments. Since the electric power that can be supplied to the thermal head is limited, the above-described time division technique cannot be applied as is to the battery-driven printer. Specifically, since an amount of electric power used increases as the time width of the electric power pulse increases, it is necessary to further increase the number of time divisions for driving thermal head. As a result, the transporting speed of the recording paper further decreases. When the transporting speed of the recording paper decreases too much, there is a possibility that the printing quality deteriorates, because clogging or the like might occur as a result of the rotation speed of a drive motor, such as a stepping motor, decreasing below the minimum rotation speed required for stable rotation.